The long-term objective of the project is the development of an effective behavioral weight control program for obese patients with Type II diabetes. The proposed project is designed to determine whether larger weight losses and more significant improvements in glycemic control can be produced by a) utilizing a 50-week behavior modification program (rather than the usual 10-20 week program), b) combining behavior modification with the use of the Very Low Calorie Diet (VLCD), and c) reintroducing the VLCD later in the program. The VLCD Is a 400 kcal/day diet of high quality protein, that has been shown to be safe and to produce large initial weight losses, but maintenance of these losses has been poor. By combining the VLCD with behavior modification and by reintroducing the VLCD at a later period, weight loss and maintenance may be improved. To test this, 108 obese subjects with Type II diabetes will be randomly assigned to treatment conditions that involve 50 weeks of behavior therapy combined with either 0, 1, or 2 bouts of the VLCD. The effect of treatment on weight, HbA, glucose tolerance and insulin secretion will be assessed. In addition, this study will analyze the effect of a rigid diet (the VLCD) on the relapse process and prospectively study relapse behaviors in general. Food diaries collected throughout the 50- week program, and interviews conducted at monthly intervals will be used to determine the effect of the VLCD on lapses from the diet, reactions to these lapses, and subsequently of relapse. The effect of the VLCD on mood, hunger, and food preferences will be studied. The proposed project will also examine the relationship between weight loss and improvements in both glycemic control and CHD risk factors, and will investigate pretreatment individual differences that may affect these relationships.